1. Field of Invention
The present invention relates to a source calibration technology, and more particularly to a metal volume source calibration phantom and a calibrating method thereof, which can directly use metal volume source calibration phantoms with different densities to derive the calibration curve for density and counting efficiency, such that according to the counting efficiency from the multi-density source calibration phantom corresponding to the density of the sample of nuclear wastes to be tested, accurate measurement results can be obtained when measuring the counting efficiency for samples of different nuclear waste materials.
2. Related Art
Currently, waste curie monitors, being substantially an assembly of several large-area plastic scintillation detectors, are frequently used for measuring the gross gamma radioactivity of very low radioactive wastes. The monitors are advantageous in its high radioactive sensitivity, high counting efficiency, short counting interval required for counting a sample, no restriction to the volume of the waste to be monitored thereby, and capability of revealing the weight of the waste monitored thereby, and so on.
However, the current waste curie monitors and the calibrating method thereof still have the following shortcomings: (1) a nonmetal calibration phantom is used for measuring the counting efficiency; however, since noncombustible metal wastes upon deregulation are mostly measured in practice, a large error exists between a nonmetal phantom and a metal waste in terms of mass attenuation coefficient and self-shielding effect, and the result of the counting efficiency measurement deviates from the actual value; (2) usually, a single substance is used in the monitor to establish density efficiency, and the fact that the sample is not made up of a single substance is neglected; (3) in the current calibration phantom, metal or nonmetal materials are arranged in a gapless manner, which is different from the loose arrangement of metal wastes, leading to a large error in the result of the counting efficiency measurement; and (4) when calibration phantoms made of different nonmetal materials and with different densities are used to derive the calibration curve, since the phantoms with different densities need to be fabricated using different materials respectively, a long period of time is required for fabricating the phantoms, and certain space is required for storing the finished phantoms, which considerably consumes time and storage space.
Therefore, it is necessary to provide a metal volume source calibration phantom and a calibrating method thereof to solve the problems encountered in the prior art.